European allies continue supporting an airline backed by Iran’s Revolutionary Guard Corps despite extended protests by the U.S.

A slew of European and Asian nations agreed in July 2015 — shortly before President Obama’s nuclear deal with Iran — to allow terror-linked Mahan Air to begin commercial flights. Routes through 15 countries, including Denmark, France, Germany, and Italy have frustrated U.S. lawmakers. Adding insult to injury for the Obama administration was a decision last week in which terror-linked Bank Saderat (accused by the U.S. of transferring money to Hamas) had sanctions lifted by the EU.

Emanuele Ottolenghi, a foreign policy expert at the Foundation for Defense of Democracies, told the Associated Press on Wednesday that Europe’s policy dissolves diplomatic leverage needed for Iran’s involvement in Syria’s civil war.

“By letting Mahan in, the Europeans are forgoing a critical pressure tool they have in their arsenal of nonmilitary coercive measures to pressure Iran and [Syrian President Bashar] Assad,” said Mr. Ottolenghi.

California Rep. Brad Sherman concurred.

“How many dead Syrians does it take for the Europeans to think there is a threat?” the Democrat asked, AP reported.

A U.S. Treasury official told the news agency on condition of anonymity that planes belonging to Mahan Air arrive in Syria on almost a daily basis.

“We’re not saying Mahan Air assists the IRGC; we’d say Mahan Air is the IRGC — and we have to give notice to our friends in Europe,” Mr. Sherman added. “This idea that we can allow Mahan Air to do whatever it wants just because there are temporary restrictions on the nuclear deal — that wasn’t the deal.”

Mahan Air, which has denied U.S. allegations, declined to speak to AP for its story.

An EU spokeswoman told AP that the U.S. has no jurisdiction on the matter.